1. Field of the Invention
Embodiments of the invention relate to a touch sensing device coupled with a display device and a method for driving the same.
2. Discussion of the Related Art
User interface (UI) is configured so that users are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices as they desire. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technologies have continuously evolved to increase user's sensibility and handling convenience. The user interface has been recently developed to touch UI, voice recognition UI, 3D UI, etc., and the touch UI has been basically installed in portable information devices. A touch screen is installed on a display panel of household appliances or the portable information devices, so as to implement the touch UI.
A capacitive touch screen has greater durability and definition than an existing resistive touch screen and is able to carry out multi-touch recognition and proximity-touch recognition. Hence, the capacitive touch screen may be applied to various applications. Because the capacitive touch screen is attached to the display panel or is embedded in the display panel, the capacitive touch screen is electrically coupled with the display panel. The display panel and the touch screen may be time-division driven in a display panel drive period and a touch screen drive period. Because a data voltage having a relatively large swing width is supplied to data lines of the display panel in the display panel drive period, a load of the display panel increases.
A current path between an output channel of a data driving circuit and the data lines of the display panel is cut off during the touch screen drive period. Hence, the data lines are floated, and are in a high impedance state or are held at DC voltage. Thus, the load of the display panel during the touch screen drive period is less than the load of the display panel during the display panel drive period. During the display panel drive period, a gate pulse (or scan pulse), which swings between a gate high voltage and a gate low voltage, is supplied to gate lines (or scan lines) of the display panel. During the touch screen drive period, the gate lines of the display panel may be held at the DC voltage, for example, the gate low voltage.
The gate low voltage supplied to the gate lines of the display panel changes because of a load difference between the display panel drive period and the touch screen drive period. For example, when the gate low voltage supplied to the gate lines of the display panel is −10V in the touch screen drive period, the gate low voltage of the gate lines is measured to almost −10V because the load of the display panel is small in the touch screen drive period. On the other hand, when the gate low voltage supplied to the gate lines of the display panel is −10V in the display panel drive period, the gate low voltage measured in the gate lines increases to almost −8V because of the large load of the display panel.
The gate low voltage supplied to the gate lines of the display panel may greatly change in a period, which changes from the display panel drive period to the touch screen drive period and vice versa, because of the load difference between the display panel drive period and the touch screen drive period. When the gate low voltage greatly changes, a noise of a voltage sensed from the touch screen greatly changes due to electrical coupling between the touch screen and the display panel. The noise reduces the sensing sensitivity of the touch screen.